This review aims to provide a historical reference of branched-chain amino acid (BCAA) metabolism and provide a link between peripheral and central nervous system (CNS) metabolism of BCAAs. Leucine, isoleucine, and valine (Leu, Ile, and Val) are unlike most other essential amino acids (AA), being transaminated initially in extrahepatic tissues, and requiring interorgan or intertissue shuttling for complete catabolism. Within the periphery, BCAAs are essential AAs and are required for protein synthesis, and are key nitrogen donors in the form of Glu, Gln, and Ala. Leucine is an activator of the mammalian (or mechanistic) target of rapamycin, the master regulator of cell growth and proliferation. The tissue distribution and activity of the catabolic enzymes in the peripheral tissues as well as neurological effects in Maple Syrup Urine Disease (MSUD) show the BCAAs have a role in the CNS. Interestingly, there are significant differences between murine and human CNS enzyme distribution and activities. In the CNS, BCAAs have roles in neurotransmitter synthesis, protein synthesis, food intake regulation, and are implicated in diseases. MSUD is the most prolific disease associated with BCAA metabolism, affecting the branched-chain α-keto acid dehydrogenase complex (BCKDC). Mutations in the branched-chain aminotransferases (BCATs) and the kinase for BCKDC also result in neurological dysfunction. However, there are many questions of BCAA metabolism in the CNS (as well as the periphery) that remain elusive. We discuss areas of BCAA and BCKA metabolism that have yet to be researched adequately.

In this study we tested the hypothesis that green tea extract (GTE) would improve muscle recovery after reloading following disuse. Aged (32 mo) Fischer 344 Brown Norway rats were randomly assigned to receive either 14 days of hindlimb suspension (HLS) or 14 days of HLS followed by normal ambulatory function for 14 days (recovery). Additional animals served as cage controls. The rats were given GTE (50 mg/kg body wt) or water (vehicle) by gavage 7 days before and throughout the experimental periods. Compared with vehicle treatment, GTE significantly attenuated the loss of hindlimb plantaris muscle mass (-24.8% vs. -10.7%, P < 0.05) and tetanic force (-43.7% vs. -25.9%, P <0.05) during HLS. Although GTE failed to further improve recovery of muscle function or mass compared with vehicle treatment, animals given green tea via gavage maintained the lower losses of muscle mass that were found during HLS (-25.2% vs. -16.0%, P < 0.05) and force (-45.7 vs. -34.4%, P < 0.05) after the reloading periods. In addition, compared with vehicle treatment, GTE attenuated muscle fiber cross-sectional area loss in both plantaris (-39.9% vs. -23.9%, P < 0.05) and soleus (-37.2% vs. -17.6%) muscles after HLS. This green tea-induced difference was not transient but was maintained over the reloading period for plantaris (-45.6% vs. -21.5%, P <0.05) and soleus muscle fiber cross-sectional area (-38.7% vs. -10.9%, P <0.05). GTE increased satellite cell proliferation and differentiation in plantaris and soleus muscles during recovery from HLS compared with vehicle-treated muscles and decreased oxidative stress and abundance of the Bcl-2-associated X protein (Bax), yet this did not further improve muscle recovery in reloaded muscles. These data suggest that muscle recovery following disuse in aging is complex. Although satellite cell proliferation and differentiation are critical for muscle repair to occur, green tea-induced changes in satellite cell number is by itself insufficient to improve muscle recovery following a period of atrophy in old rats.

In vitro muscle contractile function assays are important to characterize the differences between different muscle types (e.g., slow vs. fast), between a diseased and non-diseased muscle, or importantly, to demonstrate the efficacy of a muscle treatment such as a drug, an overexpressed transgene, or knockout of a specific gene. Fundamental contractile properties can be assessed by twitch, tetanic, force-frequency, force-velocity, and fatigue assays. Many of these assays are conducted with the muscle at a constant length, e.g., an isometric contraction. However, to better represent the dynamic purpose of muscles in vivo (e.g., to move limbs), dynamic assays such as the force-velocity (concentric contractions) or stretch-injury (eccentric contractions) should also be obtained. Characterizing skeletal muscle function in vitro is a powerful approach to demonstrate efficacy of a treatment to rescue diseased muscle and to assess functional regeneration.

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A novel function for L1 cell adhesion molecule and its interaction with Ankyrin, an actin-spectrin adaptor protein, was identified in constraining dendritic spine density on pyramidal neurons in the mouse neocortex. In an L1-null mouse mutant increased spine density was observed on apical but not basal dendrites of pyramidal neurons in diverse cortical areas (prefrontal cortex layer 2/3, motor cortex layer 5, visual cortex layer 4).The Ankyrin binding motif (FIGQY) in L1’s cytoplasmic domain was critical for spine formation, as demonstrated by increased spine density in the prefrontal cortex of a mouse mutant (L1YH) harboring a tyrosine to histidine mutation in this motif, which disrupts L1-Ankyrin association. This mutation is a known variant in the human L1 syndrome. In both mutants mature mushroom spines rather than immature spines were predominant. L1 was detected in spines and dendrites of wild-type prefrontal cortical neurons by immmunostaining. L1 coimmunoprecipitated with Ankyrin B (220 kDa) from cortical lysates of wild-type but not L1YH mice. Spine pruning assays in cortical neuron cultures from wild-type and L1YH mutant mice showed that the L1-Ankyrin interaction mediated spine retraction in response to the class 3 Semaphorins, Sema3F and to a lesser extent Sema3B. These ligands also induce spine pruning through other L1 family adhesion molecules, NrCAM and Close Homolog of L1 (CHL1), respectively. This study provides insight into the molecular mechanism of spine regulation and underscore the potential for this adhesion molecule to regulate cognitive and other L1-related functions that are abnormal in the L1 syndrome.

A novel function for the L1 cell adhesion molecule, which binds the actin adaptor protein Ankyrin was identified in constraining dendritic spine density on pyramidal neurons in the mouse neocortex. In an L1-null mouse mutant increased spine density was observed on apical but not basal dendrites of pyramidal neurons in diverse cortical areas (prefrontal cortex layer 2/3, motor cortex layer 5, visual cortex layer 4. The Ankyrin binding motif (FIGQY) in the L1 cytoplasmic domain was critical for spine regulation, as demonstrated by increased spine density and altered spine morphology in the prefrontal cortex of a mouse knock-in mutant (L1YH) harboring a tyrosine (Y) to histidine (H) mutation in the FIGQY motif, which disrupted L1-Ankyrin association. This mutation is a known variant in the human L1 syndrome of intellectual disability. L1 was localized by immunofluorescence staining to spine heads and dendrites of cortical pyramidal neurons. L1 coimmunoprecipitated with Ankyrin B (220 kDa isoform) from lysates of wild type but not L1YH forebrain. This study provides insight into the molecular mechanism of spine regulation and underscores the potential for this adhesion molecule to regulate cognitive and other L1-related functions that are abnormal in the L1 syndrome.

Nuclear Nrf2 showed a significant in the trained group compared to sedentary group across all muscles (69.5%, p = 0.04), with no difference in cytosol Nrf2. SOD1 increased in the cytosol fraction in trained (18%, p = 0.04) compared to sedentary group. KEAP1 content showed no change in the cytosol. HO1 showed no difference in concentration in the muscles. CONCLUSIONS:The results from this study showed that exercise training induced nuclear translocation of Nrf2 in the muscles tested with no change in KEAP1 concentration. SOD1 in the cytosol increased but HO1 did not suggesting selective increases in the downstream antioxidants. Further research is needed to understand Nrf2 nuclear translocation with endurance training. Future studies should examine Nrf2-DNA binding and determine mRNA of Nrf2-related genes.

Postnatal regulation of dendritic spine formation and refinement in cortical pyramidal neurons is critical for excitatory/inhibitory balance in neocortical networks. Recent studies have identified a selective spine pruning mechanism in the mouse prefrontal cortex (PFC) mediated by class 3 Semaphorins and the L1-CAM cell adhesion molecules Neuron-glia related CAM (NrCAM), Close Homolog of L1 (CHL1), and L1. L1-CAMs bind Ankyrin B (AnkB), an actin-spectrin adaptor encoded by Ankyrin2 (ANK2), a high confidence gene for autism spectrum disorder (ASD). In a new inducible mouse model (Nex1Cre-ERT2: Ank2flox: RCE), Ank2 deletion in early postnatal pyramidal neurons increased spine density on apical dendrites in PFC layer 2/3 of homozygous and heterozygous Ank2-deficient mice. In contrast, Ank2 deletion in adulthood had no effect on spine density. Sema3F-induced spine pruning was impaired in cortical neuron cultures from AnkB-null mice and was rescued by re-expression of the 220 kDa AnkB isoform but not 440 kDa AnkB. AnkB bound to NrCAM at a cytoplasmic domain motif (FIGQY1231), and mutation to FIGQH inhibited binding, impairing Sema3F-induced spine pruning in neuronal cultures. Identification of a novel function for AnkB in dendritic spine regulation provides insight into cortical circuit development, as well as potential molecular deficiencies in ASD.